Gaussian Blur. I dont use the dodge/burn tool because I cant control it well enough. So I just use the airbrush tool combined with the gaussian blur filter. This allows me to create a smooth transistion between two colors. You can see an example of the final results at http://members.home.net/arioch/pm.htm

Well, The best way for me to do that is using the smudge tool (opacity:22) small brush. And the other tool I use for that is the spray in "multiply" with the color you need! Give it a try, it works for me!

it's really handy to become quick as anything with switching brush sizes.
or develop enough control to use pressure to change the brush size.
either way correcting burn and dodge edges is tricky.
you can sample the colour of the burned area and use a non-additive tool like airbrush
(which is pretty much what Affected and Reclife are saying)